(1):

(v. t.) To exert physical or intellectual strength for the attainment of; to use efforts to effect; to strive to achieve or reach; to try; to attempt.

(2):

(n.) An exertion of physical or intellectual strength toward the attainment of an object; a systematic or continuous attempt; an effort; a trial.

(3):

(v. i.) To exert one's self; to work for a certain end.